Software Defined Network (SDN) is different from conventional networks in that it has a separated control plane and network forwarding plane. The network forwarding plane does not have control functions, and the control plane may be controlled by an operating system independent from the forwarding plane. Characteristics may be customized in the operating system.
OpenFlow is one example of a standard defining communication interfaces between controllers and forwarding layer in an SDN architecture. OpenFlow allows direct access and controlling of the forwarding plane of network devices. The network devices may be physical devices or virtual devices.
According to SDN, the control plane and the data plane are separated, and communicate with each other using defined protocols. The data plane forwards data based on flow.